Viscous properties of heavy oil and bitumen make such products difficult and expensive to extract from underground reservoirs. Techniques used to recover the products include thermal and solvent based recovery processes that reduce viscosity of the products in-situ in order to enable flow of the products into production wells. Gravity drainage of the reservoirs once the products are made mobile relies on ability to have vertical fluid flow.
Economic viability for any recovery method depends on amount of hydrocarbons recoverable as determined by thickness of the reservoirs. However, inter-bedded impermeable layers act as barriers to vertical flow compartmentalizing multiple stratified reservoirs that are developed independent of one another. While as a collective group the stratified reservoirs may have sufficient thickness to be economical for production, the impermeable layers limit applicability of the recovery processes, such as cyclic steam stimulation (CSS), steam assisted gravity drainage (SAGD), vapor extraction (VAPEX), and in-situ combustion (ISC).
Vertical wells allow contact with each of the stratified reservoirs but are often not produced at economic rates. Horizontal wells expose an areal extent of the reservoir to a wellbore and enable recovery corresponding to the areal extent. Even with horizontal or undulating wells, the impermeable layers isolating the areal extent from other reservoirs above or below the impermeable layers may limit viability for economic production.
Therefore, a need exists for improved methods and systems for oil recovery from formations having reservoirs separated vertically by a stratum less permeable than the reservoirs.